1. Field of Invention
The present invention relates to a method for fabricating a pixel structure. More particularly, the present invention relates to a method for fabricating a pixel structure requiring less photomasks.
2. Description of Related Art
A thin film transistor liquid crystal display (TFT-LCD) consists of a thin film transistor array substrate, a color filter array substrate, and a liquid crystal layer, and the thin film transistor array substrate consists of a plurality of thin film transistors (TFTs) arranged in an array and the pixel electrodes configured corresponding to each of the TFTs. The above TFT includes a gate, a semiconductor layer, a source, and a drain. The TFT and the pixel electrode constitute a pixel structure. The TFT acts as a switching element for the liquid crystal display unit.
When fabricating a TFT, the most important consideration is to reduce the number of process steps, thereby reducing the manufacturing costs. Especially, if the number of photomasks required by the process steps can be reduced, the manufacturing costs can be significantly reduced.
FIGS. 1A-1G are schematic cross-sectional views of processing steps of a conventional method for fabricating a pixel structure. Referring to FIG. 1A, first, a gate 110 is defined on a substrate 100 using a first photomask (not shown). Next, referring to FIG. 1B, a gate insulating layer 120 is formed on the substrate 100 to cover the gate 110.
Then, referring to FIG. 1C, a semiconductor layer 130 is defined on the gate insulating layer 120 above the gate 110 using a second photomask (not shown), and the semiconductor layer 130 includes a channel layer 132 and an ohmic contact layer 134. Then, referring to FIG. 1D, a metal layer (not shown) is formed on the substrate 100, and a source 142 and a drain 144 are defined through a third photomask (not shown). Particularly, at this time, a back channel etching (BCE) process is carried out to remove the ohmic contact layer 134 sandwiched between the source 142 and the drain 144, as shown in FIG. 1E.
Then, referring to FIG. 1F, a protective layer 150 is formed over the substrate 100, and the protective layer 150 is patterned using a fourth photomask (not shown), and the protective layer 150 has an opening 152 exposing the drain 144. Afterwards, a transparent conductive layer (not shown) is formed over the substrate 100. A pixel electrode 160 is defined through a fifth photomask (not shown), and is electrically connected to the drain 144 through the opening 152. Thus, the pixel structure 200 is completed.
Generally, five photomasks are required for patterning by the conventional fabricating processes for the pixel structure 200. Therefore, it is desirable to reduce the number of photomasks required for the fabricating processes, so as to lower the manufacturing costs.